1. Field of the Invention
The present invention relates to a system target decoder, and in particular to a capacity of an audio buffer used in a decoder for reproducing a stream obtained by conducting multiplexing so that an audio skew generated in a stream connection portion will not be separated from a video stream corresponding thereto.
2. Description of the Related Art
In the MPEG2 system standards, a STD (system target decoder) is defined for each of PS (program stream) and TS (transport stream) as a virtual decoder model, in order to separate individual elementary streams (video streams and audio streams) from packet multiplexed streams, and decoding, synchronizing, and displaying them.
In the MPEG2 system standards, however, there are no stipulations concerning a method for connecting a plurality of independent streams and reproducing them seamlessly.
In Part 3: DVD-Video standards included in standards concerning a DVD (digital versatile disk), therefore, an E-STD (extended system target decoder) is defined as an extended decoder model in order to allow a user to conduct seamlessly manipulations such as directors cut and multi-angle.
A stream for seamless reproduction is divided into units called interleave units, and disposed in a recording area called an interleave block. At the time of reproduction, among the interleave units, interleave units which are not specified by the user are jumped. Only the interleave units specified by the user are read out, and continuously inputted to the E-STD.
This E-STD is premised on a recording system in which an audio skew generated in a connection portion of the sream is separated from a video stream (to be subjected to synchronous reproduction) corresponding to it, and multiplexed. It is now assumed that as streams following a certain stream SI three interleave units, angle 1, angle 2 and angle 3 are prepared because of a multi-angle configuration as shown in FIG. 1. In this case, audio skews generated in connection portions between the stream S1 and the angles 1, 2 and 3 are separated from a video stream included in the stream Si, and multiplexed to the angles 1, 2 and 3.
In such a recording system, however, there occurs a problem that data differing in reference time for decoding and display are mixedly present in the angle 1, angle 2 and angle 3 shown in FIG. 1 and consequently the logical structure thereof becomes indefinite.
Furthermore, in locations differing from a stream boundary, the stream is cut off. A cluster of data obtained by the cut off (such as the stream S1, and angles 1, 2 and 3 shown in FIG. 1) is herein referred to as xe2x80x9cclipxe2x80x9d. As shown in FIG. 2, boundaries between clips do not coincide with boundaries between streams. This results in a problem that the meaning of boundaries becomes indefinite. Especially in the case where individual clips are managed as files by a personal computer or the like, an audio skew and a video stream corresponding to it are contained in separate files, resulting in a hindrance to file management.
On the other hand, by adopting such a recording system that audio skews generated in connection portions of a stream are multiplexed so as not to make them separate from a video stream corresponding thereto, the above described problems can be avoided.
As the system target decoder for conducting seamless reproduction of a stream in such a recording system, however, it becomes necessary to increase the capacity of an audio buffer included in hardware resources of the P-STD defined by the MPEG2 system standards. Or while maintaining the hardware resources intact, it becomes necessary to conduct software processing for temporally changing an area of a single buffer assigned as a video buffer and an area of the single buffer assigned as an audio buffer. The reason will be described later.
In the system target decoder increased in audio buffer capacity, an object of the present invention is to stipulate the capacity of the audio buffer to be increased.
In an audio buffer used in a decoder for reproducing a stream obtained by conducting multiplexing so that an audio skew generated in a stream connection portion will not be separated from a video stream corresponding thereto, the capacity of the audio buffer is increased, in the present invention, according to an increase value of the data storage amount in an interval during which an audio stream is inputted to this audio buffer, but a video stream is not inputted to a video buffer of this system target decoder.
According to the present invention, the capacity of the audio buffer is increased by the above described amount. As a result, a system target decoder system for conducting seamless reproduction of a stream obtained by conducting multiplexing so that an audio skew generated in a stream connection portion will not be separated from a video stream corresponding thereto can conduct reproduction without causing overflow from the audio buffer.